Justification:
Wild-caught sources of this species were once an important food fish in Thailand, Lao PDR, Cambodia, and Vietnam. Roberts (1993) notes the disappearance of wild adults from Thailand during the 1980s and early 1990s. Adult individuals are still present in the Chao Phraya in small protected areas near temples, but the population status outside these protected areas is unclear (Z. Hogan pers. comm. 2011). Vidthayanon (pers. comm. 2011) states that, in the Chao Phraya River basin, the species now only exists as escapee or semi-captive populations. The species has also been extirpated from the Mekong in Thailand due to overfishing of adults (C. Vidthayanon pers. comm. 2011).

By the early 1990s, the Mekong River Commission (MRC 1992) reported that the species remained abundant only in Cambodia. More recently, there are indications that the size of Cambodian populations have also dropped dramatically. Cambodian fishers (age 40+, n=43) estimate that overall catch of the species has declined by 68% since 1980 (Hogan et al. unpub. data). Individually, many fishers report that catch per fisher has declined by as much as 99% since 1980 from several tons per season to 10-100 kg per season (Hogan et al. unpub. data). Fishers in the Tonle Sap River report that catches of the species have dropped by 90% in the largest fishing lots of the Tonle Sap Lake – from about 100 tonnes 20 years ago to just five or even one tonne today (Hogan pers. comm. 2010). Similarly, Van Zalinge et al. (2002) reports 108-165 billion fry captured in the Cambodian dai fishery in 1981, 5.0-12.0 billion in 1991, and just 2.0-4.0 billion in 1997. These data suggest a strong decline in numbers despite constant effort (Van Zalinge et al. 2002). And while adult fish are still present in the fishery, they are becoming rarer. Fishers have not caught the largest class of fish (35-80 kg) since 1972. Fishers in the Tonle Sap River bagnet fishery #2 reported 97 mature fish in 2004, 222 in 2005, and 3 in 2006.

As a large-bodied, commercially valuable, migratory species, this fish is particularly vulnerable to ongoing threats from over-exploitation, habitat degradation (including changes in water quality and flow), and fragmentation of river habitat. Based on reduction in extent of occurrence (nearly extirpated from the Chao Phraya and Thai Mekong), decline in past abundance (and expected future declines arising from continued exploitation and habitat decline resulting from potential hydro-power dam development on the mainstream of the Mekong) the species is assessed as Endangered (A2bcd+A4bcd).

Note that this species is cultivated on a large scale throughout the region. Baird et al. 2004 noted that although the species was almost absent from catches at the Khone Falls in the 1990, except for 1995, when a sharp increase in juveniles was recorded, and suggests that this may have been the result of large numbers of captive-bred juveniles being released downstream in Cambodia during a period of political instability. This suggests that the population might recover rapidly if fishery pressure on the wild population were to be reduced.

This species occurs in the Chao Phraya and middle-lower Mekong basins (Rainboth 1996), and is also reported from the Mae Khlong in Thailand. It is a very common aquaculture species, especially in Viet Nam and Thailand. It has been introduced widely outside of its native range, and has established populations in, for example, Myanmar (Ayeyarwaddy River) and Indonesia.

Wild populations of this specieswere once an important food source in Thailand, Lao PDR, Cambodia, and Viet Nam. Roberts (1993) noted the disappearance of wild adults from Thailand during the 1980’s and early 1990’s. By the early 1990’s, this species remained abundant only in Cambodia (MRC 1992). There are indications that Cambodian populations have dropped dramatically in 2006. Cambodian fishermen (age 40+, n=43) estimate that overall catch of this fish has declined by 68% since the 1980’s (Z. Hogan, unpublished data). Individually, older fishers report that catch per fisher has declined by as much as 99% since 1980 from several tons per season to 10-100 kg per season. In the largest fishing lots of the Tonle Sap Lake, catches of the species have dropped by over 90% – from about 100 tons 20 years ago to just five or even one ton today. While adult fish are still present in the fishery, fishers have not caught the largest class of fish (35-80 kg) since 1972. Fishers in the Tonle Sap River bagnet reported 97 adult fish in 2004, 222 in 2005, and three in 2006. Once common in breeding sites in Chao Phraya basin, it is now rare and only escapee or semi-captive populations are common.

Despite declining wild populations, the species remains a common and popular aquaculture species in Thailand, Cambodia, and Vietnam with thousands of tons produced annually.

The species is a large, fecund, relatively slow growing catfish. It is an omnivore, feeding primarily on algae, plants, zooplankton, insects, fruits, crustaceans, and fish. It inhabits main channels and floodplains of large rivers and seasonally moves up to floodplains and marshland for feeding and nursing.

Life historyThis fish grows approximately one kilogram per year (Khanh 1996, Lenormand 1996). Van Zalinge (2002) suggests size at first reproduction to be approximately at 3.5 kg or 60 cm. Khanh (1996) and Xuan (1994) published similar estimates of approximately 112,000 to 138,000 eggs per kilogram body weight after age four. River catfish reach full maturity after age ten. Absolute maximum fecundity is 2,000,000 (Khanh 1996). Mortality rates are difficult to estimate, because of the complicated life history of the river catfish. Many factors, including reproductive ecology, small egg size, and high fecundity suggest that the species is adapted to high mortality of early life stages. Maximum life span is estimated at approximately 20 years (pangasiids at the Steinhart Aquarium in San Francisco, U.S.A. are 20 years old). The fish reaches full maturity between two and four years. The best estimate of generation length is between 10 and 15 years (Z. Hogan, pers. comm. 2010).

Movement PatternsIn the Mekong River basin, the species is thought to move out of the Tonle Sap Lake, up the Mekong River, and into deep pool areas to spawn in northeastern Cambodia at the beginning of the rainy season (between May and July). In 2002, ultrasonic and conventional tagging provided clear evidence of long distance migration in the Mekong River basin (Hogan et al. 2006). A catfish (first tagged and released in the Tonle Sap River on November 30, 2001) was recaptured in the Mekong River 320 km upstream of Phnom Penh, Cambodia. The movement indicates that the species is capable of migrations in excess of 300 km. Given reports that this and many other Mekong species spawn in northern Cambodia, this movement was likely a spawning migration. These data, when assessed together with data on the migrations of a closely related species, Pangasius krempfi, which migrates over 700 km, (Hogan et al. 2007), provide strong evidence that pangasiid catfish are capable of long distance movements. The movement of fish from the Tonle Sap River floodplain to deep-water pools in the upper Cambodian Mekong may represent a critical step in the life history of this and several other species. Deep-water areas are recognized as important dry season refuges for many fishes in the Mekong River basin. In the Cambodian Mekong, the species spawns between May and July. The young fish drift downstream to the lower reaches of the Cambodian Mekong and into the Tonle Sap Lake.

The species, including eggs and fry, are heavily exploited. Annual harvests have been estimated to be as much as 100,000 to 150,000 tons per year (MRC 1992; Csavas 1994), although culture of pond-stocked fry accounts for the majority of this production (MRC 1992). Until recently, an estimated 200,000,000 to one billion eggs and fry are collected annually from Cambodia and Viet Nam. Juveniles of this species are popular for aquarium trade.

Overexploitation, habitat degradation, and changes in water quality and flow are the major threats to the species. Though once a staple food throughout its range, it has been heavily exploited and exploitation, combined with other factors, has led to the near extinction in the Chao Phraya River in Thailand and the Thai Mekong. In Cambodia, mature fish populations are in decline. Future plans to dam the Mekong could disrupt the species life cycle because the species is migratory and appears to rely on flow or water quality to facilitate migrations, cue spawning, and aid in the dispersal of young fish.

The species has been bred in captivity and this may reduce pressure on stocks of wild fish. Some measures have been put in place in Cambodia to limit the harvest of fry. Semi-captive populations exists in small no fishing zones adjacent to temples in Thailand.